Late is an adjective and an adverb, describing an event that happened after the correct time:
(the usual time for breakfast is earlier, around 7-9 AM)
(the bus arrived thirty minutes after the correct time on the schedule)
Avoid this common error: if you arrive late for an appointment, don’t say “Sorry for late” or “Sorry for the late.” The correct expression is “Sorry I’m late.”
Delay is a noun and a verb, describing a cause for something to be late:
(the traffic caused us to be late)
(the miscommunication caused the project to fall behind schedule)
Postpone is a verb – it is when you choose to do something at a later time than planned. Usually “delay” involves factors beyond your control (like the traffic or weather), whereas “postpone” is a more conscious decision to change the schedule.